Patent EP 742 236 describes petrol tanks consisting of five layers which are, respectively:                high density polyethylene (HDPE);        a binder;        a polyamide (PA) or a copolymer containing ethylene units and vinyl alcohol units (EVOH);        a binder;        HDPE.        
A sixth layer can be added between one of the layers of binder and one of the HDPE layers. This sixth layer consists of manufacturing scraps following moulding of the tanks, and to a much smaller extent of non-compliant tanks. These scraps and non-compliant tanks are then ground until granules are obtained. This ground material is then remelted and extruded directly at the tank coextrusion plant. This ground material may also be melted and regranulated by means of an extruding machine such as a twin-screw extruder, before being reused.
According to one variant, the recycled product can be mixed with the HDPE from the two extreme layers of the tank. It is possible, for example, to mix the granules of recycled product with granules of virgin HDPE of these two layers. It is also possible to use any combination of these two recyclings. The content of recycled material can represent up to 50% of the total weight of the tank.
Patent EP 731 308 describes a tube comprising an inner layer comprising a mixture of polyamide and of polyolefin with a polyamide matrix and an outer layer comprising a polyamide. These tubes based on polyamide are useful for transporting petrol and more particularly for bringing the petrol from the motor vehicle tank to the motor and also, but in larger diameter, for transporting hydrocarbons in service stations between the distribution pumps and the underground storage tanks.
According to another form of the invention, a layer of a polymer comprising ethylene units and vinyl alcohol units (EVOH) can be placed between the inner and outer layers. The structure: inner layer/EVOH/binder/outer layer is advantageously used.